1. Field of the Invention
This invention relates to an electronic apparatus which is capable of retaining stored data in a memory during interruption of power supply thereto, with the aid of a memory backup power source.
2. Discussion of the Prior Art
In conventional electronic apparatus of the foregoing type, generally, the data stored in a memory, such as a random access memory, is retained by the use of a memory backup power source when power to the apparatus is interrupted. In order to ascertain whether the content of the memory is accurately retained or not at the time power is again supplied to the apparatus, it was heretofore customary to execute this step by accessing check data written previously at a partial storage position in the memory, then, deciding, in accordance with the correctness or incorrectness of the check data thus accessed, the validity of the desired data written at other storage positions in the memory, and producing an error signal in case any error was detected from the check data. However, if the voltage of the memory backup power source was reduced to near the threshold value of a data retaining voltage, at the time of interruption of power to the apparatus, the desired data may become destroyed in the memory even though the check data was retained validly therein. Thus, disadvantageously, exact decision on the validity of the desired data is not attainable by discriminating the check data at the time of resumption of power.
Furthermore, in another conventional apparatus of a type equipped with additional circuitry for checking the data retaining voltage of a memory backup power source during interruption of the power supply, there also exist various disadvantages, such as higher production costs due to use of such additional circuitry, increased power consumption in the memory backup power source, and shortening of the total backup time for the memory.
Accordingly, there is still certain deficiencies which need correcting in backup power sources used for memory upon interruption of power supply to the apparatus using such memories.